Floating aquatic plants such as the plants of the duckweed family have the capability of rapidly taking up nutrients from an aquatic environment to provide a food source with a high nutritional and protein content. When grown on the surface of a waste water treatment pond, duckweed serves an important water purification purpose while producing a harvestable feed crop. However, in order to enable efficient commercial utilization of the duckweed species it must be capable of being utilized in large bodies of water. A floating aquatic plant does not attach itself to the bottom of the pond or other body of water on which it is growing and is subject to wave action when grown on the surface of large bodies of water. The wave action will push the aquatic plants to a localized area, causing the destruction of the plants and reducing their growth and reproduction efficiency as the surface contact with the nutrients in the water is reduced. To maximize the growth and reproduction of the floating aquatic plants it is essential that they be evenly dispersed over the surface of the water to maximize their surface contact with the water.
An aquatic biomass containment barrier is disclosed in U.S. Pat. No. 4,536,988 incorporated by reference herein. This containment barrier operates to reduce the effect of wave action on the small plants by dividing the surface of the body of water into a large number of relatively small surface area compartments divided by flexible, buoyant plastic sheets formed into a network of rectangular compartments and held together by metallic clips. The duckweed are harvested by submerging the buoyant barriers beneath a common weed harvester.
To provide a barrier system which is more resistant to environmental conditions and repeated harvestings, and which may be rapidly deployed and taken in, it would be advantageous to form a barrier from a plurality of identical horizontally extending sturdy plastic parts.
These horizontally extending plastic barrier members should be joined to one another by pin-connected hinges for maximum resilience of the barrier network. However, due to the long moment arms of the barrier members and the repeated and high intensity loads placed on them, the hinges must be able to withstand significant loads.
All-plastic hinges are well known to the art. Plastic hinges are typically formed by an injection molding process since it is necessary to achieve thickened portions of the hinges at the hinge knuckle as compared to the hinge leaves. Injection molding, while suitable for small parts, is inordinately expensive for very large articles of manufacture such as a barrier member which is typically on the order of six to ten feet long.
The twin-sheet thermoforming process is a cost effective method of producing large plastic parts. Twin-sheet thermoformed articles, however, are normally limited to either a single or a double thickness wall at any point on the article. Unreinforced twin-sheet thermoformed parts cannot economically form hinged knuckles of sufficient strength to bear the necessary loads of an aquatic biomass containment barrier. Under the prior art metal or plastic hinges formed by some other process must be attached with fasteners to the thermoformed article.
There is a need for an economical, one-piece, all-plastic containment barrier member which may be hingedly connected into a network for raising and harvesting floating aquatic plants.